Dampener for offset lithographic printing



April 2, 1957 '5. w. HUBBARD DAMPENER FOR OFFSET LITHOGRAPHIC PRINTINGFiled Sept. 50, 1954 INVENTCR. Bruce Hubbard ATTORNEYS United StatesPatent DAMPENER FOR OFFSET LITHOGRAPHIC PRINTING Bruce W. Hubbard, OakPark, Ill., assignor to Ideal Roller and Manufacturing Company, Chicago,Ill, a corpora fion of Illinois Application September 30, 1954, SerialNo. 459,258

2 Claims. (Cl. 101-447) This invention relates to the so-called dampenerroll used in offset lithographic printing to receive water from a ductorroll and wet the nonsensitized areas of the lithographic plate duringoperation of the offset lithographic printing press.

The general object of the invention i to provide a dampener surfacewhich is much less costly than the so-called molleton surface now incommon use, which possesses improved water receptive characteristics,and which may be removed and replaced easily and quickly without thenecessity of removing the supporting roller from the printing press.

Another object is to provide an improved dampener roll having a thinwater receptive covering mountable on a base roll by simply wrapping aflexible sheet of the covering material around the roll.

A further obiect is to achieve cheapness and ease of repiaceabilitythrough the use of sheetmaterial composed of cellulose fibers initiallycombined in a paper making machine.

Still another object is to provide a water receptive element composed ofcellulose fibers joined or reinforced by a nonfibrous substance whichpossesses adequate wet strength and is suificiently water pervious topermit of use of the composite sheet as the covering for a dampenerroll.

Other objects and advantages of the invention will become apparent fromthe following detailed description taken in connection with theaccompanying drawings, in which Figure l i a schematic view showing theelements of an offset lithographic printing press with the dampener rollconstructed in accordance with the present invention.

Fig. 2 is a cross section of the dampener roll.

Fig. 3 is a perspective view illustrating the manner of applying thedampener roll covering.

In the operation of an offset lithographic printing press, the printingplate having sensitized and nonsensitizcd areas 11 and 12 is Wrappedaround and attached to a rotary cylinder 1% whose surface is contactedcontinuously by an inking roller 13 and a water roller 14. The latterruns in contact with and receives water from a rigid roll which in mostofiset lithographic printing presses is vibrated axially back and forthand operates to wet the nonprinting areas 32 of the lithographic plateso as to confine the transfer of ink from the roll 13 to the plate areas11 from which the ink is transferred to a blanket to on a roll whichmakes the printing impression on a sheet 13 backed by the impressionroll 19. The base 23. of the water roll is usually composed ofrelatively firm rubber or other yieldable material.

The present invention contemplates the provision on the dampener roll 14of a covering 263 which possesses improved water receptive properties ascompared to the surfaces heretofore used and which at the same time maybe applied in the form of a rectangular sheet by wrapping or spiralingaround the circumference of the roller base 21. The attainment of thesenew results is based on my 2,787,213 Fatented Apr. 2, 1957 discoverythat so-called vegetable parchment paper possesses unusual waterreceptive properties as Well as other characteristics not recognized orutilized heretofore but correlated closely with the requirements for adampener roller covering in offset lithographic: printing. These unusualproperties are developed in the initial formation of the paper andso-called parchmentizing of part of the cellulose fibers.

A soft highly absorbent sheet is first formed in an ordinary papermaking process during which the cellulose fibers, although interlockingeffectually with each other, tend to aline themselves along the lengthof the paper or the direction of advance through the paper-makingmachine. The so-called waterleaf thus formed is passed quickly through abath of carefully controlled regenerating chemical, usually sulphuricacid, which immediately attacks the sheet dissolving some of the fibersinto a jelly or gelatin-like substance known as amyloid. This substancefills up the pores and effectually cements the remaining fibers into acohesive mass.

After momentary immersion in the acid bath, the sheet is washed free ofacid to interrupt the parchmentizing action after which the sheet isdried in the usual way. While the paper thus parchmentized may be ofdifferent weights and thicknesses, it is preferred to employ a sheetweighing about 15 pounds per 1,000 square feet.

Paper formed in the above manner has been found to be unusually waterreceptive, that is, capable of absorbing and holding a substantialquantity of water. This is believed to be due to the fact that asubstantial part of the fibers of the original paper remain unchanged inthe short acid treatment and, perhaps due to the somewhat porouscharacter of the amyloid cementing them together, these fibers arereadily accessible for absorbing a substantial amount of water. At thesame time, no loose fibers are exposed on the paper surface and thelatter remains completely lint free-an important requirement of adampener surface.

The paper also possesses ample strength when wet to withstand the forcesto which the surface is subjected while running in contact with theplate and adjacent steel cylinders of an offset lithographic printingpress. The amyloid cement is believed to be responsible for thisimportant characteristic since it is a non-fibrous substance possessinguniform tensile strength in all directions particularly when reinforcedby the cellulose fibers that become embedded in the parchmentizingprocess.

A final characteristic utilized in practicing the invention is theability of the paper sheet to adapt itself accurately to the convexcurvature of the base roller periphery and form itself into a smoothunwrinkled layer of uniform thickness in spite of the fact that thetrailing end of the sheet overlaps the remainder of the sheet and isleft exposed after the wrapping. To mount the sheet and form such acovering, advantage is taken of the tendency of the paper, when it iswet, to stretch enough in all directions to adapt itself to the contourof the roll and thus eliminate any wrinkles that may exist in the sheetinitially or after Wrapping around the base roll. With some papers theavoidance of wrinkles in the final wet covering may be facilitated bytaking advantage of the tendency of the paper to curl in a directiontransversely of the length of the fibers 23 (Fig. 3) which, in the paperforming process, tend to aline themselves in the direction of advance ofthe sheet during its formation. When wetted, there is some tendency forthe sheet to curl in a direction perpendicular to the fibers.Accordingly, it is sometimes desirable, though not essential, to arrangethe sheet on the base roller so that the fibers 23 parallel the rolleraxis.

While the paper sheet may be fastened to the roll at its leading edge22, it has been found that no securing means is actually required. Thus,the preferred procedure in forming the covering 20 is to first cut apaper sheet of a length substantially equal to the axial length of thebase roll and of a width somewhat greater than the roll circumference.One edge 22 of the sheet is laid along the roller periphery parallel tothe axis 24. The roller is then turned in the direction in which itrevolves during actual printing thus Winding or Wrapping the sheetaround the roll with the trailing end 27 overlapping the initially laidpart of the sheet as shown in Fig. 2. By Wetting the paper andcontinuing the turning slowly while the roll is in contact with theadjacent steel roll 15, any wrinkles in the sheet will be ironed outautomatically and disappear completely leaving the Wrapped around layertightly contracted around the base and secured frictionally againstturning relative to the latter. At the same time, the trailing endportion and the initially .laid or underlying part of the sheet becomeso matted together that the end 27 virtually disappears leaving a smoothsurface which, in spite of the double thickness ever part of thecircumference, is sufliciently uniform in diameter to provide propercontact at all times With the surface of the plate cylinder duringactual printing.

One thickness of the paper covering the base roll has been found to besufiicient to provide the desired dampening action. If desired, however,the sheet may be made long enough to extend two or even more timesaround the base roll.

The dampener constructed as above described possesses numerousadvantages over the so-called molleton now in common use. Most importantis the improved quality of the printing which has been noted due to theunusual manner in which Water is absorbed, retained, and distributedover the printing plate surface. The Wet covering has been found topossess ample strength to resist the frictional forces to which it issubjected in ordinary service use in an otfset lithographic printingpress even when the Water transfer roller is vibrated axially through asubstantial range. The cost of the paper sheet both initially and forreplacement in service is only a small fraction of the cost of molletonsleeves. In fact, the cost of the entire covering is so small that itmay be disposed of and replaced frequently thus avoiding the high laborand equipment costs heretofore involved in cleaning and replacing theexpensive molleton fabric. Finally, since the covering is discardedafter one use, it may be stripped off from the base while the latterremains in the press. Then, since the covering is applied in the form ofa sheet wrapped around the base, it may be renewed without disassemblyof the press or roller mounting. These advantages combine to overcome aserious handicap Which has been recognized for years in the offsetprinting art.

I claim as my invention:

1. An offset lithographic printing press having, in combination, a platecylinder carrying a sensitized lithographic printing plate, and adampener roll for said plate comprising a base, a resiliently yieldablecovering thereon,

and a thin sheet of vegetable parchment paper snugly wrapped around saidcovering with the trailing end of the sheet left free, said sheetpresenting a continuous water receptive outer surface for contactingsaid printing plate.

2. An offset lithographic printing press having, in combination, a platecylinder carrying a sensitized lithographic printing plate, and adampener roll for said plate comprising a base, a resiliently yieldablecovering thereon, and a thin sheet of vegetable parchment paper snuglyWrapped around said covering and presenting a continuous water receptiveouter surface contacting said printing plate.

References Cited in the file of this patent UNITED STATES PATENTS683,478 Meyer Oct. 1, 1901 1,972,448 Jenkins Sept. 4, 1934 1,976,039Rowell Oct. 9, 1934 2,230,981 Toland et a1. Feb. 4, 1941 2,312,853Toland et al Mar. 2, 1943 2,530,388 Gullixson Nov. 21, 1950

